1. Field of the Invention
The present invention relates to a power module structure and, more particularly, to a power module structure including a smoothing capacitor for smoothing a DC supply voltage to be externally applied to a power semiconductor device such as an IGBT.
2. Description of the Background Art
FIG. 28 is a schematic top plan view of a structure of a background art power module body portion 100. Output terminals 111U, 111V and 111W are arranged along a first side of a top surface of a case frame 106, and a P-terminal 108P and an N-terminal 108N are arranged along a second side of the top surface of the case frame 106 which is parallel to the first side.
FIG. 29 is a cross-sectional view showing a cross-sectional structure taken along the line X100—X100 of FIG. 28. The case frame 106 made of resin is disposed on a base plate 101 made of metal. A case lid 116 made of resin is disposed on the case frame 106. An insulating substrate 102 made of ceramic is soldered, as shown at 103, onto the base plate 101. A plurality of power semiconductor devices 105 such as IGBTs are soldered, as shown at 104, onto the insulating substrate 102. Circuit elements (not shown) such as switching elements are mounted on the top surface of the insulating substrate 102, and a predetermined circuit pattern (not shown) is formed on the top surface of the insulating substrate 102.
A control substrate 114 formed with a control circuit for controlling the power semiconductor devices 105 is disposed within the case frame 106. The control substrate 114 is soldered to first ends of respective interconnection electrodes 112. Second ends of the respective interconnection electrodes 112 are connected through aluminum wires 109 to the power semiconductor devices 105. An anti-noise shield plate 113 is disposed between the control substrate 114 and the insulating substrate 102 within the case frame 106. An interior space of the case frame 106 below the shield plate 113 is filled with a silicone gel 115.
The N-terminal 108N is disposed on the top surface of the case frame 106. The N-terminal 108N is connected to a first end of an N-electrode 107N. A second end of the N-electrode 107N is connected through the aluminum wires 109 to the power semiconductor devices 105. The P-terminal 108P (not shown in FIG. 29) is also disposed on the top surface of the case frame 106. The P-terminal 108P is connected to a first end of a P-electrode 107P. A second end of the P-electrode 107P is connected to the power semiconductor devices 105 through the aluminum wires 109 and the circuit pattern formed on the insulating substrate 102. The output terminal 111V is disposed on the top surface of the case frame 106. The output terminal 111V is connected to a first end of an output electrode 110. A second end of the output electrode 110 is connected through the aluminum wires 109 to the power semiconductor devices 10S.
FIG. 30 is a schematic cross-sectional view showing the overall construction of a background power module, as viewed in side elevation. A smoothing capacitor 120 for smoothing a DC supply voltage to be externally applied to the power semiconductor devices 150 is disposed over the power module body portion 100. An N-electrode 121N and a P-electrode 121P (both designated by the reference numeral 121 in FIG. 30) of the smoothing capacitor 120, and the N-terminal 108N and the P-terminal 108P (both designated by the reference numeral 108 in FIG. 30) of the power module body portion 100 are connected to each other through a connecting conductor 124. The connecting conductor 124 has conductor plates 122N and 122P opposed to each other, with an insulation plate 123 therebetween. The conductor plates 122N, 122P and the N- and P-terminals 108N, 108P are fastened to each other with respective screws 125.
FIG. 31 is a schematic cross-sectional view showing a structure of connections between the smoothing capacitors 120 and the connecting conductor 124, as viewed in top plan. The conductor plate 122N is in contact with the N-electrodes 121N, and the conductor plate 122P is in contact with the P-electrodes 121P. The conductor plate 122N has openings 126 provided partially to avoid contact with the P-electrodes 121P, and the conductor plate 122P has openings 127 provided partially to avoid contact with the N-electrodes 121N.
However, the above-mentioned background art power module requires the connecting conductor 124 including the conductor plates 122N, 122P and the insulation plate 123 for connection between the N- and P-electrodes 121N, 121P of the smoothing capacitors 120 and the N- and P-terminals 108N, 108P of the power module body portion 100. This presents problems in the large number of parts and in complicated assembly.
Another problem is an increased circuit inductance because of a long wiring path between the smoothing capacitors 120 and the power semiconductor devices 105. In the operation of the power module, the high-speed switching of the power semiconductor devices 105 causes a large pulse-shaped current proportional to the amount of current change (di/dt) to flow between the smoothing capacitors 120 and the power semiconductor devices 105, thereby to develop a voltage proportional to the circuit inductance, which in turn is applied as noise to the power semiconductor devices 105. Further, the increase in circuit inductance requires the increase in electrostatic capacitance of the smoothing capacitors 120 for suppression of ripple voltage. This results in the increase in the size of the smoothing capacitors 120 and accordingly the increase in the size of the power module itself. Therefore, the circuit inductance is preferably low.
Furthermore, the background art power module which comprises the large-sized smoothing capacitors 120 disposed over the power module body portion 100 is too low in resistance to vibration for use as a vehicle-mounted power module, for example.